1. Field of the Invention
The present invention relates generally to a vehicular driving characteristics control system, such as a suspension control system, a power steering control system, rear wheel steering angle control system in an four wheel steering system. More specifically, the invention relates to a vehicular driving characteristics control system which controls vehicular driving characteristics depending upon vehicular steering angular position. Further particularly, the invention relates to a fail-safe system for a vehicular driving characteristics control system which performs fail-safe operation in response to failure of steering angle sensor and/or a detector detecting steering neutral position.
2. Description of the Background Art
Japanese Patent First (unexamined) Publication (Tokkai) Showa 62-77210 discloses a vehicular steering angle monitoring system. The disclosed system includes means for monitoring vehicular steering behavior to generate a steering data. Based on the generated steering data, a steering neutral position indicative data is projected. The system is also provided with a steering neutral position sensor to detect steering angular position approximately at a predetermined neutral position to produce a neutral position signal. Based on the projected steering neutral position data and measured approximate neutral position, a center value of a steering neutral range is projected.
The steering angular displacement relative to the projected center value of the steering neutral range is monitored for performing control for controlling vehicular driving characteristics, such as anti-rolling suspension control, adjustment for power assist for a power steering system, adjustment of rear wheel steering angle in a four wheel steering system and so forth are performed.
In such conventional vehicular driving characteristics control system, means for detecting steering neutral position, such as steering neutral switch, is essential element. Therefore, when the steering neutral position detecting means fails, it becomes impossible to project the center value of the steering neutral range or to accurately project the center value. This causes in accuracy of detection of the steering angle displacement and thereby cause error in vehicular driving characteristics control.